The ruse? Trading off the penalty rates and casual loadings of vulnerable, low paid workers in exchange, in many cases, for barely a handful of coins in extra hourly pay.Tens of thousands of workers are worse off as a consequence.

It defies belief that Coles and the SDA didn’t know that they were agreeing to a deal that left some low paid workers as much as $3500 a year short of their entitlements.

The landmark Fair Work Commission decision is a stunning indictment, finding that the deal with Coles did not pass the “better off overall test”.

Put simply, this is the legal requirement that workers should be paid more in a workplace agreement than they are under the award, the basic safety net of wages and conditions.

This is not the only questionable deal inked by the “shoppies” union with big retailers.

It is likely up to half a million workers in Australia are being underpaid due to cosy deals struck between big companies and the SDA. That includes agreements struck with Woolworths and McDonald’s.

Just over a week ago Fairfax Media revealed that some workers at McDonald’s were nearly a third worse off than the award with underpayment across the company of at least $50 million a year.

Both ACTU secretary Dave Oliver and Labor leader Bill Shorten have been running a campaign to “protect” penalty rates this federal election.

But instead of a sober self-assessment in the wake of the commission’s decision, all we got on Tuesday was evasion and pathetic spin from Oliver.

He defended the McDonald’s agreement (where young workers on $10 an hour are being underpaid) and said the commission’s decision in the Coles case showed the system is “working”.

It only ‘worked’ because the cosy deal was exposed by Fairfax Media a year ago, helped by the courage and research skills of an official from another union, Josh Cullinan.

The promise to protect penalty rates now looks like a sad joke from a labour movement with too few union members and far too many unions dominated by political hacks masquerading as officials.

Working conditions in Australia for low paid vulnerable workers, particularly temporary foreign workers, are getting worse. In nearly all cases there is no union representing them.

When the union is the SDA, sadly, vulnerable workers are probably better off with no union at all.

The benefit for the SDA in striking these deals is that the big employers are happy to have their representatives on site, signing up members.

That gives it influence in Labor, where the Catholic-dominated SDA uses its numbers to try block social policy change such as marriage equality. On the back of young workers, this union bolsters its conservative social agenda.

As for Coles, the third largest employer in Australia has successfully re-branded itself with slick ads, cheap milk and store makeovers.

But one thing hasn’t changed. In collusion with the SDA it has been ripping its workers off for years. Those worst off? The most vulnerable. The young, and those on casual and part time shifts.